Method of producing a hard metal



Reissued Feb. 25, 1941 UNITED STATES PATENT OFFICE Paul Schwarzkopf, Yonkers,

N. Y., assignor to American Cutting Alloys, Inc., New York, N. Y., a corporation of Delaware N 0 Drawing.

Original No. August 22, 1939, Serial No.

2,170,433, dated 164,166, September 16, 1937. Application for reissue August 6, 1940, Serial No. 351,639. In Germany May 16, 1929 i 8 Claims.

This invention refers to a hard metal tool alloy and method of producing the same.

This invention forms a continuation in part of my copending application Ser. No. 727,781, filed May 26, 1934, and of my copending application Ser. No. 743,717, filed September 12, 1934 and issued into Patent No. 2,122,157, which were in turn copending with my application Ser. No. 656,103, filed February 10, 1933 and issued into Patent No. 1,959,879, and my application Ser. No. 625,042, filed July 27, 1932 and issued into Patent No. 2,091,017, which were in turn copendlng with my application Ser. No. 452,132, filed May 13, 1930 and I of course do not claim herein anything which is subject matter of the claims in my above mentioned earlier patents.

It is an object of the invention to increase the hardness of such hard metal tool alloys without impairing their toughness.

It is another object of the invention to increase the resistance of such hard metal tool alloys against mechanical wear and chemical effects such as of the oxygen of the surrounding air, or moisture, or a cooling liquid such as water.

It is another object of the invention to adjust the heat conductivity of the hard metal tool alloy without impairing its hardness or resistance against oxidation.

It is still another object of the invention to increase the speed at which hard alloys, of this kindcan be used for cutting, drilling, milling, and other machining purposes.

This and other objects of the invention will be more clearly understood when the specification proceeds.

Hard metal tool alloys have been made of tungsten carbide and auxiliary metal taken substantially from the iron group, in amounts from about 3% to 20%. The tungsten carbide has been finely powdered and mixed with the auxiliary metal, and the mixture heated to sintering temperature. Such hard metal tool alloys could be utilized for machining cast iron but do not prove efllcient in high speed machining steel and other compositions of metal.

In contradistinetion hereto the invention proceeds from fundamentally new considerations. It no longer uses one carbide alone, viz. tungsten carbide, and cements it by auxiliary metal in the heat.

The present invention particularly refers to a method of producing a hard metal composition, comprising a consolidated product consisting substantially of about 3% to 22% auxiliary metal essentially of the iron group, and at least two carbides of tungsten, molybdenum (i. e. an element of the sixth group of the periodical system), boron (i. e. an element of the third group of the periodical system), titanium (i. e. an elea ment of the fourth group of the periodical system) and vanadium (i. e. an element of the fifth group of the periodical system) and in general of at least two hard carbides of different elements selected from the third, through sixth groups of the periodical system. The invention comprises the steps of comminuting, preferably as finely as possible, at least two hard carbides selected from pable of forming such structures, in addition to atoms of carbon required to form carbide with those elements. Experiments have shown and science has given the rule that the hardness of solid solutions of elements is a function of their proportion, and that this function possesses a maximum. choose for use in the present invention homogeneous carbide crystal structures as defined above exhibiting approximately maximum hardness and thereby increase the overall or average hardness of the composition.

Let me take the rules given by the science based on the investigations of Kurnakow and Zemczuzny in the Zeitschrift fiir anorganische Chemie 1908, volume 60, page 1, and 1910, volume 68, page 136, referred to in the standard book of Reinglass Chemische Technologie der Legierungen", second edition, page 52,53, and in the Metallund Legierunskunde. of Dr. M. v. Schwarz, Professor of the College at Munich, second edition (1929), page 49, where the 111- vestigations of Kurnakow are referred to and it is verbatim stated:

In an uninterrupted series of mixed crystals 1. e. solid solutions the curve of hardness increases with the concentration gradually up to a fiat maximum, which lies mostly at the simple atomic composition. If Schwarz says atomic composition," it is to be considered that he mentions metals and not chemical compounds such as car- It is particularly advantageous to instead of atoms, which exist only of the pure metals, the molecules are to be taken, because they are in compounds equivalent to the atoms,

of the pure metal.

Furthermore, science says that the maximum does not always lie at simple molecular proportions. If one element materially exceeds another element in hardness, then the maximum of hardness is fshifted in favor of the harder element in the solid solution and consequently two (or three) atoms form together with one atom of the softer element the solid solution of greatest hardness. By analogy, according to the invention the carbides are to be present approximately in integer number ratios of their molecular weights, the higher ratio applying to the relatively harder carbide, if one of the composed carbides is harder than the other. Lastly, if a curve of hardness of solid solutions .is built up depending on the content of the respective carbides, then the maximum of the curve is flat and i does not form a tip so that solid solutions of about greatest hardness are practically also obtained if.

deviating by about 5% to 10% to both Sides from the theoretical molecular proportion corresponding togreatest hardness.

' Let me take an alloy having 10% auxiliary metal and therefore 90% carbide. Let me further assume that tungsten-carbide and titaniumcarbide are to be compounded to form the hardest composition. Then we have to divide these 90% in the proportion of 60: 196, this means that we have to take about 20% (by weight) titaniumcarbide, about 70% tungsten-carbide and about.

10% auxiliary metal.

Let metake molybdenum-carbide and titanium-carbide. hard, at least considerably harder than molybdenum-carbide and is furthermore very light. Consequently the optimum of hardness is to be expected at a proportion of about 1:3. At 1:3 we have about 49.5 (that means less than 50%) molybdenum-carbide and 40.5% titanium-carbide, if 10% auxiliary metal is present.

Let me take vanadium-carbide (carbide of the fifth group) and titanium-carbide (carbide of the fourth group). Considering that titaniumcarbide exceeds vanadium-carbide in hardness, the molecular proportion'is to be chosen with about 1:2 and consequently the hard metal will containabout 60% titanium, carbide and about 30% vanadium carbide in.order to remain within the range of hardest compositions, if 10% auxiliary metal are present.

Let me take, as last example, boron carbide (of the third group) and titanium carbide (of the fourth group). Boron carbide is known as one of the hardest carbides. is investigated as BC with a molecular weight of '18. Assuming that the hardness of both carbides is about the same, the solid solution has to be made of about equal proportion of about 78:60. Consequently, an alloy will c ntain about 50% boron carbide and about40 titanium carbide, if'10% auxiliary metal are present.

Hard metals of the above compositions particularly exhibit high resistance against oxidation at elevated temperature, great hardness and relamount of auxiliary metal essentially of the iron group may vary between about 3% and 22%.

The amount may be smaller if heavy mixtures of Titanium-carbide is exceedingly The boron carbide 5 bides. If such compounds are to be used, then carbides (e. g. tungstem, molybdenum carbide) are concerned and larger if lighter mixtures of carbides (e. g. with titanium carbide) are concerned.

As a consequence of the considerations presented, the following compositions selected admixed and compounded according to the invention exhibit great hardness: 10% to 20% vanadium carbide, 85% to tungsten carbide, 5% to 20% auxiliary metal; 50% to titanium carbide, 45% to 25% vanadium carbide, 5% to 25% auxiliary metal; 60% to 40% titanium car- Y bide, 55% to 35% boron carbide, 5% to 25% auxiliary metal; 10% to 25% titanium carbide, to 55% tungsten carbide, 5% to 20% auxiliary metal; 35% to 60% tantalum carbide, 35% to 60% tungsten carbide, 5% to 20% auxiliary metal; 70% to 90% tantalum carbide, 5% to 25% vanadium carbide, 5% to 20% auxiliary metal; 65% to tantalum carbide, 10% to 30% columbium carbide, 5% to 20% auxiliary metal; 25% to 40% vanadium carbide, 55% to 70% columbium carbide, 5% to 20% auxiliary metal.

For special purposes, e. g. for finest cuts or polishing mixtures of titanium carbide and'molybdenum carbide in about equal proportions forming substantially homogeneous carbide crystal structures or solid solutions and nickel up to .9% and 15% and chromium up to 1% and 2% as auxiliary metalshas been proven advanta geous. I

If solid solutions of more than two carbides are to be contained in the composition, one proceeds with advantage insuch a way that first at least two groups of binary solid solutions are formed, each group comprising different carbides, whereupon these groups are combined into ternary or quaternary solid solutions and by sintering in the presence of the auxiliary metal. Those groups of solid solution are preferably formed before addition of substantial amounts of auxiliary metal,

It is satisfactory for the structures or solid solutions are produced. Ac-

invention if only sub-v stantial amounts of homogeneous carbide crystal cording to experience already about 10% of the It is quite difficult to mention any minimum amount of carbide to be present, because 5% titanium-carbide occupy a space four times as large as 5% by weight of tungstenscarbide. Nevertheless, the minimum amount of carbide to be present and forming part of homogeneous carbide crystal structures or solid solutions has to be substantial, and as a minimum, about 1% by weight of the alloy. v

The carbides produced are, if needed, powdered and intimately and uniformly mixed with the chosen auxiliary metal or. metals. The mixtures are then preformed by pressing in suitable moulds to a shape similar to the desired shape. The shrinking which takes place during the following treatment must be taken into calculation.

An electric furnace can be employed for effecting the heating am sintering; the slntering may also be carried out by means of high frequency currents. In some cases particularly good results are obtained by carrying out the heating or sintering in a vacuum.

The temperature of the body is to be elevated to about 1400 to 1600 C. and this heat-treatment is to be continued for about one or several hours, or a major part of one hour, till the desired structure according to the invention is produced.

Generally, the body according to my invention is consolidated by using auxiliary metals of the kind and in the amounts as mentioned before and sintering it at elevated temperature, e. g. in the range up to about 1400 C. to 1600 C. until solid solutions or homogeneous carbide crystal structures as hereinbefore defined, are formed.

In case, however, difiicult forms of the body are to be produced not achievable by usual moulds, or in case sharp edges are desired, or angles difficult to manufacture in such a way, so thatthe mechanical working or finishing of the hard metal body is needed after sinten'ng, then the following way is preferable.

The pressed and preformed body is to be submitted to sintering temperatures as mentioned before, but such slntering should be done during a short period of time only, say for 1 to Etc 10 minutes so that the particles are sufficiently fritted together to withstand mechanical treat-' ment without presenting, however, the hardness of a fully sintered body. Such a body is then subjected to finishing in any way and then the sintering at the same temperature is continued until the sintered body answering the invention is achieved.

When I refer in the appended claims to carbide of elements selected from the third, fourth, fifth and sixth group of the periodical system, I mean carbides adapted for use in hard tool elements,-

having a suitable hardness and not being dissolved by water or other cooling or similar purposes at operation temperatures. Such carbides are boron-oarblde (belong ing to the third group), titanium-carbide (belonging to the fourth group), vanadium-carbide, columbium carbide, tantalum-carbide (belonging to the fifth group), and tungsten-carbide, molybdenum-carbide (belonging to the sixth .group) Tool alloys prepared according to the invention are, as a rule, not used for the production of the entire tool, but merely for the part of the tool which in practice is used directly for cuting, drilling, etc. and which is subject to wear.

From the above description it appears that the carbides are compounded entirely or in substantial amount into solid solutions or homogeneous carbide crystal structures as hereinbefore defined, in the presence of auxiliary metal essentially of the iron group and byheat treatment to suilicient extent, while cementing of the composition is effected. It has been found that homogeneous carbide crystal structures or solid solutions resist re-crystallization to a great extent. Thereby finest grain of carbides present I in the alloy including those structures is retained, and a tough and very efiicient, clean cutting material is obtained.

If carbides highly resistant to oxidation and other carbides less'resista'nt to oxidation are thus compounded according to the invention into solid solutions or homogeneous carbide crystal structures as hereinbefore defined, the re sistivity of those structures against oxidation surpasses that of the carbide of originally lower resistivity.

What I claim is:

1. In a method of producing a hard metal alloy, in particular for tool elements and other working appliances, the steps of commlnutlng liquid employed for as finely as possible at least two hard carbides formed therein in substantial amount.

2. In a method of producing a hard metal composition, in particular for toolelements and other working appliances, the steps of finely comminuting at least two hard carbides of different elements selected from the third through sixth group of the periodical system, admixing said comminuted carbides in substantial amounts, including a minimum of 1% of a selected carbide, with auxiliary metal essentially of the iron group in amounts of about 3% to 22%, shaping and pressing said mixture and finally alloying it by sintering into a hard and solid body and until solid solutions of said selected carbides are formed therein in substantial amount.

3. In a method of producing a hard metal al- Joy, in particular for tool elements and other working appliances, the steps of comminuting as finely as possible at least two hard carbides of different elements selected from the third, fourth, fifth and sixth group of the periodical system, admixing said comminuted carbides in substantial amounts, including a minimum of 1% of a selected carbide, with auxiliary metal essentially or the iron group in amounts of about 3% to 22%, shaping said mixture and finally alloying it by sintering into a hard and tough body and until solid solutions of said selected carbides are formed in substantial amount and increase thereby the average hardness of the alloy,

at. In a method of producing a hard metal alloy, in particular for tool elements and other working appliances, the steps of comminuting as finely as possible at least two hard carbides of different elements selected from the third, fourth, fifth and sixth group of the periodical system, admixing said comminuted carbides in substantial amounts, including a minimum of 1% of a selected carbide, with auxiliary metal essentially of the iron group in amounts of about 3% to 22%, shaping and pressing said mixture and finally alloying it by sinteiing into a hard and tough body and until substantial amounts of said selected carbides form solid solutions and increase thereby the average hardness of the alloy.

5. In a method of producing a hard metal composition, particularly for tool elements and other working appliances, the steps of selecting and finely comminuting at least two hard carbide crystal structures formed from carbon and different element selected from at least two different groups of the periodical system the third through sixth group thereof, admixing the comgeneous carbide crystal structures are obtained therein containing atoms of at least two elements atoms.

6. In a method oi producing a hard metal composition, particularly for tool elements and other working appliances, the steps of selecting and comminuting as finely as possible at least two carbide crystal structures formed from carbon and different elements selected from the group consisting of boron, titanium, vanadium, columbium, tantalum, tungsten, molybdenum, admixing the comminuted carbide structures in sub stantial amounts, including a minimum of about 1% of a selected carbide structure, with auxiliary metal essentially of the iron group inamounts of about 3% to 22%, shaping said mixture and finally compounding it by sintering at temperatures between about 1400" and l600 C. until a hard and tough body and substantial amounts of homogeneous carbide crystal structures are obtained therein containing atoms of at least two elements selected from said group in addition to carbom atoms, and the average hardness of the composition is increased thereby.

'i. In a method of producing a hard metal composition, in particular for tool elements and working appliances, the steps 01'. finely comminuting a carbide crystal structure containing titanium in addition to carbon and another carbide crystal structure containing tungsten in addition to carbon, admixing said comminuted carbide structures in substantial amounts, including a minimum oi 1%. of a carbide structure, with auxiliary metal essentially of the iron group in amounts of about 3% to 22%, shaping said mixture and finally compounding it by sintering into a hard and tough body until substantial amounts of homogeneous carbide crystal structures are obtained therein, containing atoms of titanium and tungsten in addition to carbon atoms.

8. In a method of producing a hard metal alloy, in particular for tool elements and workin appliances, the steps of comminuting as finely as possible at least two hard carbides oi diflerent elements selected from at least two different groups of the periodical system the third through sixth group thereof, admixing said commlnuted carbides in substantial amounts, including a minimum of 1% of a selected carbide, and in proportions suitable to yield approximately hardest homogeneous carbide crystal structures containing atoms 0! at least two elements selected from said groups in addition to carbon atoms, with auxiliary metal essentially of the iron group in amounts of about-3% to 22%, shaping said mixture and finally alloying it by sintering into a hard and tough body and until said crystal structures are formed in substantial amount.

PAUL SCHWARZKOPF. 

